Compositions and articles comprising polymerizable ionic liquid mixture, and methods of curing

ABSTRACT

Presently described are curable compositions comprising a mixture of at least one (e.g. free-radically) polymerizable ionic liquid and at least one other ethylenically unsaturated monomer, oligomer, or polymer. The polymerizable ionic liquid is characterized as having an air to nitrogen curing exotherm ratio of at least 0.70. Also described are articles and methods of making articles from such curable compositions. A monofunctional polymerizable ionic liquid is also described comprising a non-polymerizable substituted imidazolium cationic group and a polymerizable sulfonate anion.

BACKGROUND

Ionic liquids (ILs) are salts in which the cation and anion are poorlycoordinated. At least one of the ionic components is organic and one ofthe ions has a delocalized charge. This prevents the formation of astable crystal lattice, and results in such materials existing asliquids, often at room temperature, and at least, by definition, at lessthan 100° C. For example, sodium chloride, a typical ionic salt, has amelting point of about 800° C., whereas the ionic liquidN-methylimidazolium chloride has a melting point of about 75° C.

Ionic liquids typically comprise an organic cation, such as asubstituted ammonium or a nitrogen-containing heterocycle, such as asubstituted imidazolium, coupled with an inorganic anion. However,species have also been described wherein the cation and anion areorganic. When the ionic liquid comprises at least one polymerizablegroup, such ionic liquid is a polymerizable ionic liquid (“PIL”).

SUMMARY

Presently described are curable compositions comprising a mixture of atleast one (e.g. free-radically) polymerizable ionic liquid and at leastone other ethylenically unsaturated monomer, oligomer, or polymer. Thepolymerizable ionic liquid is characterized as having an air to nitrogencuring exotherm ratio of at least 0.70. In some embodiments, the air tonitrogen curing exotherm ratio of the polymerizable ionic liquid is atleast 0.75, 0.80, 0.85, 0.90, or 0.95. The other ethylenicallyunsaturated monomer, oligomer, or polymer typically has a substantiallylower air to nitrogen curing exotherm ratio, e.g. no greater than about0.50. The curable compositions typically comprise an initiator, such asa photoinitiator.

The presence of the polymerizable ionic liquid improves the curing ofthe composition especially in the presence of oxygen (e.g. air) withoutinerting with a gas such as nitrogen or curing between oxygenimpermeable films. The presence of the other ethylenically unsaturatedmonomer, oligomer, or polymer can improve the stability of thepolymerizable ionic liquid by hindering unintended polymerization, suchas during storage. The presence of the polymerizable ionic liquid mayalso improve the cure speed of the polymerizable composition, mayrequire reduced amounts of initiators and/or require reduced lightintensity while curing effectively in the presence of oxygen. This caprovide cured (e.g. coating) materials with faster, lower costcompositions and processes.

In some favored embodiments, the curable composition comprises amultifunctional polymerizable ionic liquid comprising at least twoethylenically unsaturated groups, optionally in combination with amonofunctional polymerizable ionic liquid. One favored multifunctionalpolymerizable ionic liquid comprises at least two ethylenicallyunsaturated groups, each bonded to the cationic group via a divalentnon-alkylene linking group. Other favored multifunctional polymerizableionic liquids comprise a polymerizable anion and a polymerizable cation.In one embodiment, the polymerizable cation comprises an aromaticmoiety. In another embodiment, the polymerizable anion comprises anaromatic moiety, such as an aromatic carboxylate anion.

In another embodiment, a monofunctional polymerizable ionic liquid isdescribed comprising a non-polymerizable imidazolium cation and a (e.g.non-fluorinated) sulfonate anion, such as

In other embodiments, articles are described such as a coated substratecomprising a substrate and a cured coating of the composition describedherein on a surface of the substrate.

In other embodiments, methods of making articles from the curablecomposition described herein are described.

DETAILED DESCRIPTION

As used herein, “hardenable” is descriptive of a material or compositionthat can be cured (e.g., polymerized or crosslinked) by heating toinduce polymerization and/or crosslinking; irradiating with actinicirradiation to induce polymerization and/or crosslinking; and/or bymixing one or more components to induce polymerization and/orcrosslinking “Mixing” can be performed, for example, by combining two ormore parts and mixing to form a homogeneous composition. Alternatively,two or more parts can be provided as separate layers that intermix(e.g., spontaneously or upon application of shear stress) at theinterface to initiate polymerization.

As used herein, “hardened” refers to a material or composition that hasbeen cured (e.g., polymerized or crosslinked).

As used herein, the term “(meth)acrylate” is a shorthand reference toacrylate, methacrylate, or combinations thereof; “(meth)acrylic” is ashorthand reference to acrylic, methacrylic, or combinations thereof;and “(meth)acryl” is a shorthand reference to acryl, methacryl, orcombinations thereof. As used herein, “a,” “an,” “the,” “at least one,”and “one or more” are used interchangeably.

Unless specified otherwise, “alkyl” includes straight-chained, branched,and cyclic alkyl groups and includes both unsubstituted and substitutedalkyl groups. Unless otherwise indicated, the alkyl groups typicallycontain from 1 to 20 carbon atoms. Examples of “alkyl” as used hereininclude, but are not limited to, methyl, ethyl, n-propyl, n-butyl,n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl,cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and thelike. Unless otherwise noted, alkyl groups may be mono- or polyvalent.

Unless specified otherwise, “heteroalkyl” includes bothstraight-chained, branched, and cyclic alkyl groups with one or moreheteroatoms independently selected from S, O, and N with bothunsubstituted and substituted alkyl groups. Unless otherwise indicated,the heteroalkyl groups typically contain from 1 to 20 carbon atoms.“Heteroalkyl” is a subset of “hydrocarbyl containing one or more S, N,O, P, or Si atoms” described below. Examples of “heteroalkyl” as usedherein include, but are not limited to, methoxy, ethoxy, propoxy,3,6-dioxaheptyl, 3-(trimethylsilyl)-propyl, 4-dimethylaminobutyl, andthe like. Unless otherwise noted, heteroalkyl groups may be mono- orpolyvalent.

Unless specified otherwise, “aromatic group” or “aromatic moiety”includes 6-18 ring atoms and can contain optional fused rings, which maybe saturated or unsaturated. Examples of aromatic groups include phenyl,naphthyl, biphenyl, phenanthryl, and anthracyl. The aromatic group mayoptionally contain 1-3 heteroatoms such as nitrogen, oxygen, or sulfurand can contain fused rings. Examples of aromatic group havingheteroatoms include pyridyl, furanyl, pyrrolyl, thienyl, thiazolyl,oxazolyl, imidazolyl, indolyl, benzofuranyl, and benzthiazolyl. Unlessotherwise noted the aromatic group may be mono- or polyvalent.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.).

Presently described are various curable compositions that comprise apolymerizable ionic liquid, comprising a cation and anion that arepoorly coordinated. Such polymerizable ionic liquids have a meltingpoint (T_(m)) below about 100° C. The melting point of these compoundsis more preferably below about 60° C., 50° C., 40° C., or 30° C. andmost preferably below about 25° C., for ease of use in variouspolymerizable compositions as described herein with or without the aidof solvent carriers in the composition. Polymerizable ionic liquidshaving a melting point below 25° C. are liquids at ambient temperature.As the molecular weight of the polymerizable ionic liquid increases, theviscosity can increase. In some embodiments, the molecular weight of thepolymerizable ionic liquid is less than 1000 g/mole.

Suitable cationic groups, also known as onium salts, include substitutedammonium salts, substituted phosphonium salts, substituted pyridiniumsalts, and substituted imidazolium salts. The structures of the cationsof such onium salts are depicted as follows:

Other cationic groups include pyrazolium, pyrrolidinium, and cholinium.

The anion may be organic or inorganic, and is typically a monovalentanion, i.e. having a charge of −1. Illustrative examples of anionsuseful herein include various organic anions such as carboxylates(CH₃CO₂ ⁻, C₂H₅CO₂ ⁻, ArCO₂ ⁻), sulfates (HSO₄ ⁻, CH₃SO₄ ⁻), sulfonates(CH₃SO₃ ⁻), tosylates, and fluoroorganics (CF₃SO₄ ⁻, (CF₃SO₂)₂N⁻,(C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, CF₃CO₂ ⁻, CF₃C₆F₄SO₃ ⁻, CH₃C₆F₄SO₃ ⁻,tetrakis(pentafluorophenyl)borate).

In some embodiments, curable (e.g. dental) compositions are describedcomprising a polymerizable ionic liquid comprising an aromaticcarboxylate anion ArCO₂ ⁻. Such polymerizable ionic liquids may comprisea (e.g. free-radically) polymerizable anion, a (e.g. free-radically)polymerizable cation, or both a (e.g. free-radically) polymerizableanion and a (e.g. free-radically) polymerizable cation. In someembodiments, the cation is a substituted ammonium, phosphonium, orimidazolium cation.

The anion may alternatively be an inorganic anion such as ClO₄ ⁻,fluoroinorganics (PF₆ ⁻, BF₄ ⁻, AsF₆ ⁻, SbF₆ ⁻) and halides (Br⁻, I⁻,Cl⁻). In some embodiments, the anion is preferably an organic anion suchas a sulfonate. Organic anions may be non-halogenated which is amenableto providing (e.g. dental) compositions that are halogen-free. In someembodiments, the (e.g. sulfonate) anion is non-fluorinated and lacks anaromatic substituent. Further, in some embodiments, the anion lacksethylenically unsaturated groups and thus is a non-polymerizable anion.In other embodiments, the organic anion is polymerizable.

The polymerizable groups are ethylenically unsaturated terminalpolymerizable groups. The ethylenically unsaturated groups arepreferably free-radically polymerizable groups including (meth)acrylsuch as (meth)acrylamide (H₂C═CHCON— and H₂C═CH(CH₃)CON—) and(meth)acrylate (CH₂CHCOO— and CH₂C(CH₃)COO—). Other ethylenicallyunsaturated (e.g. free-radically) polymerizable groups include vinyl(H₂C═C—) including vinyl ethers (H₂C═CHOCH—). The methacrylatefunctional onium salts are typically preferred over the acrylate oniumsalts in compositions because they exhibit a slower rate of cure.

The polymerizable ionic liquid functions as a reactive monomer and thusis substantially unpolymerized in the curable composition at the timethe curable composition is applied to a substrate or formed into a (e.g.dental) article, such as a dental crown. Hence, the curable compositionhardens upon curing via polymerization of the ethylenically unsaturatedgroups of the (e.g. multifunctional) polymerizable ionic liquid. Suchcuring generally results in a permanent bond. For example, when thecurable composition is an adhesive, the bonded substrate typicallycannot be separated without substrate damage.

In some favored embodiments, the polymerizable ionic liquid issufficiently low in viscosity that it acts as a reactive diluent. Insuch embodiment, the composition can advantageously be substantiallyfree of solvents, especially organic solvents. This can result inincreased efficiency with respect to manufacturing time as well asenergy consumption by reducing or eliminating drying the compositionprior to curing. This can also reduce the volatile organic content (VOC)emissions of the composition.

In some embodiments, the polymerizable ionic liquid is monofunctional,having one polymerizable ethylenically unsaturated group. Monofunctionalpolymerizable ionic liquids can be combined with conventionalmultifunctional ethylenically unsaturated (e.g. (meth)acrylate) monomersto enhance curing thereby minimizing the formation of a surface residuesurmised to be caused by oxygen curing inhibition of curablecompositions.

In other embodiments, the polymerizable ionic liquid is multifunctional,typically comprising two or three polymerizable groups. For example, insome embodiments the polymerizable ionic liquid may comprise apolymerizable cation and a polymerizable anion. In other embodiments,the multifunctional polymerizable ionic liquids described herein can becharacterized as having a multifunctional cation, having two, three, ormore polymerizable groups bonded to the same cationic group.

In some embodiments, the polymerizable ionic liquid is a mixturecomprising at least one multifunctional polymerizable ionic liquid andat least one monofunctional polymerizable ionic liquid.

The polymerizable ionic liquid(s) is typically employed in combinationwith other conventional (e.g. (meth)acrylate) ethylenically unsaturatedmonomer(s), oligomer(s), or polymer(s). By “other” is it meant anethylenically unsaturated monomer that is not a polymerizable ionicliquid. Although conventional monomers are polymerizable and many areliquids at 25° C., conventional monomers are typically non-ionic,lacking a cation and an anion.

It has been found that a polymerizable ionic liquid can be used in placeof conventional hardenable (meth)acrylate monomers, such as2-hydroxylethyl methacrylate (HEMA), triethyleneglycol dimethacrylate(TEGDMA), and 2,2-bis[4-(2-hydroxy-3-methacyloxypropoxy)phenyl]propane(BisGMA), such as commonly used in curable (e.g. dental) compositions.Such embodiment is amenable to providing a dental composition that isfree of monomer derived from bisphenol A (such as BisGMA).

Preferred (e.g. multifunctional) polymerizable ionic liquids exhibit ahigh air to nitrogen curing exotherm ratio, as can be measured by photoDSC according to the test method described in the examples. The air tonitrogen curing ratio is typically at least 0.70 or 0.75. In preferredembodiments, the air to nitrogen curing exotherm ratio is typically atleast the 0.80, 0.85, 0.90, or 0.95. For embodiments wherein the air tonitrogen curing ratio of the polymerizable ionic liquid is sufficientlyhigh, the polymerizable ionic liquid can advantageously be substantiallycompletely cured in air (i.e. an oxygen rich environment) rather thanrequiring curing in the absence of oxygen.

A completely cured (i.e. hardened) polymerizable ionic liquid is solidat 25° C. and is substantially free of uncured polymerizable ionicliquid. When significant uncured polymerizable ionic liquid is presentit typically results as a surface residue exhibiting a “wet” appearance.Minimal surface inhibition not only provides more complete curing butalso minimizes the formation of a less cured oxygen inhibited surfacelayer. This provides the benefit of reduced extractables and also lessneed to remove the uncured “wet” monomer layer by use of an absorbantwiping material with or without a solvent such as ethanol. The extent ofcuring can be determined by various methods known in art. One commonmethod is to determine the amount of uncured material by solventextraction. In preferred embodiments, the amount of uncured extractablepolymerizable ionic liquid is less than 10%, more preferably less than5%, and most preferably less than 1% by weight of the cured composition.

Conventional (meth)acrylate monomers typically have an air to nitrogencuring exotherm ratio of no greater than 0.50, 0.40, 0.35, 0.20, or 0.25or lower. For example, TEGMA has been found to have an air to nitrogencuring exotherm ratio of about 0.36; whereas HEMA has been found to havean air to nitrogen curing exotherm ratio of less than 0.25. Although thephotocuring of conventional (meth)acrylate monomers and especiallymethacrylate monomers is typically inhibited by oxygen present in air,the inclusion of the (e.g. multifunctional) polymerizable ionic liquidcan sufficiently increase the air to nitrogen curing exotherm of themixture such that the mixture can advantageously be substantiallycompletely cured in air. For embodiments wherein the composition is tobe cured in air and the multifunctional polymerizable ionic liquid iscombined with another polymerizable (meth)acrylate component thatexhibits a lower air to nitrogen curing exotherm ratio, the air tooxygen curing exotherm ratio of the (e.g. multifunctional) polymerizableionic liquid, described herein, is preferably at least 0.85, 0.90, or0.95.

The total concentration of (e.g. multifunctional) polymerizable ionicliquid(s) having a high air to nitrogen curing exotherm ratio, istypically at least 30 wt-% and preferably at least 40 wt-% of theunfilled composition (the total polymerizable organic compositionexcluding inorganic filler). In this embodiment, the total concentrationof other ethylenically unsaturated (e.g. (meth)acrylate) monomer(s),oligomer(s), and polymer(s)) is typically at least 10 wt-%, 20 wt-%, 30wt-%, 40 wt-%, 50 wt-%, or 65 wt-%.

Although the presence of the (e.g. multifunctional) polymerizable ionicliquid having a high air to oxygen curing ratio is beneficial to curing,as just described, the presence of the other conventional (meth)acrylatemonomer may also benefit the (e.g. multifunctional) polymerizable ionicliquid by improving the stability by hindering unintendedpolymerization, such as during storage, prior to (e.g. photo) curing.This is amenable to providing one-part curable coating composition.Thus, in at least some favored embodiments the amount of otherethylenically unsaturated (e.g. (meth)acrylate) monomer(s), oligomer(s)is typically at least 21 wt-%, 22 wt-%, 23 wt-%, 24 wt-%, or 25 wt-% ofthe unfilled composition. Thus, the concentration of (e.g.multifunctional) polymerizable ionic liquid(s) having a high air tooxygen curing ratio is less than 80 wt-%. Typically, it is preferred tomaximize the concentration of other ethylenically unsaturated (e.g.(meth)acrylate) monomer(s), oligomer(s) provided that the air to oxygencuring ratio of the mixture is at least 0.75 and preferably at least0.80, 0.85, 0.90 or greater. Depending on the selection of otherethylenically unsaturated (e.g. (meth)acrylate) monomer(s), oligomer(s),this concurrently can be achieved with when the concentration of (e.g.multifunctional) polymerizable ionic liquid(s) having a high air tooxygen curing ratio is at least about 35 wt-%, 40 wt-%, or 45 wt-%. Forembodiments, wherein the other ethylenically unsaturated monomer(s),oligomer(s), and polymer(s) has an air to oxygen curing exotherm ofabout 0.25 or lower, the concentration of polymerizable ionic liquid ispreferably at least 50 wt-%, 55 wt-%, or 60 wt-%.

In some favored embodiments, the curable compositions comprise a newclass or new species of polymerizable ionic liquid.

In some favored embodiments the curable composition comprises amultifunctional cation, having two or more polymerizable groups, eachbonded to the same cationic group via a divalent non-alkylene linkinggroup. Such multifunctional polymerizable ionic liquid is furtherdescribed in U.S. Provisional Application Ser. No. 61/237,992, titled,“OPTICAL DEVICE WITH ANTISTATIC COATING” and U.S. ProvisionalApplication Ser. No. 61/289,072, titled, “POLYMERIZABLE IONIC LIQUIDCOMPRISING MULTIFUNCTIONAL CATION AND ANTISTATIC COATINGS”; incorporatedherein by reference. As used herein, linking groups refer to theentirety of the chain of atoms between the (e.g. single) cation andethylenically unsaturated terminal group. Although the linking groupsmay and often comprises lower alkylene segments, e.g. of 1 to 4 carbonatoms, the linking groups further comprise other atoms within the carbonbackbone and/or other groups pendant to the (e.g. carbon) backbone. Mostcommonly, the linking groups comprise heteroatoms such as sulfur,oxygen, or nitrogen, and more commonly oxygen or nitrogen. The linkinggroups may comprise linkages such as amide (—CONR—) or ether (—COC—)linkages and more commonly urethane (—ROCONR—), urea (—RNCONR—), orester linkages (—COOR—); wherein R is a lower alkyl of 1-4 carbon atoms.

For embodiments wherein the cation is ammonium or phosphonium, thepolymerizable ionic liquid may have the general formula:

wherein:Q is nitrogen or phosphorous;R¹ is independently hydrogen, alkyl, aryl, alkaryl, or a combinationthereof;R² is independently an ethylenically unsaturated group;L¹ is independently a linking group with the proviso that at least twoof the linking groups are not alkylene linking groups;m is an integer of 2 to 4;n is an integer of 0 to 2;and m+n=4; andX is an anion.

At least two of the linking groups, L¹, are preferably linking groupsthat comprise one or more heteroatoms such as nitrogen, oxygen, orsulfur. In favored embodiments, at least two of the linking groups, L¹comprise nitrogen or oxygen heteroatoms, such as linking groups thatcomprise an amide, urea, ether, urethane or ester linkage. The linkinggroup may comprise more than one of such linkages.

Although each terminal ethylenically unsaturated group, R², bonded toeach linking group can comprise a different ethylenically unsaturatedgroup, the terminal ethylenically unsaturated group, R², is typicallythe same ethylenically unsaturated polymerizable group, such as the samevinyl, (meth)acrylamide, or (meth)acrylate group.

In some embodiments, m is 3 and thus, the polymerizable ionic liquid isa trifunctional (e.g. tri(meth)acrylate) polymerizable ionic liquid. Inother embodiments, m is 2 and thus, the polymerizable ionic liquid is adifunctional (e.g. di(meth)acrylate) polymerizable ionic liquid.

In some embodiments, n is at least 1. R¹ is typically hydrogen or astraight-chain lower alkyl of 1 to 4 carbon atoms. However, R¹ mayoptionally be branched or comprise a cyclic structure. R¹ may optionallycomprise phosphorous, halogen, or one or more heteroatoms such asnitrogen, oxygen, or sulfur.

Preferred polymerizable ionic species wherein the cation is ammoniuminclude:

These species just described can include various other anions, aspreviously described.

When such polymerizable ionic liquid is utilized in an antistaticcoating, the polymerizable ionic liquid (i.e. onium salt) may be presentin the antistatic layer at a weight percentage of 1 to 99.5%, preferably10 to 60%, and more preferably 30 to 50%. For this embodiment, the acrylfunctional polymerizable ionic liquids are preferred over the methacrylpolymerizable ionic liquid because they exhibit a faster and greaterdegree of cure.

In other embodiments, the polymerizable composition comprises an ionicliquid comprising a polymerizable cation and a polymerizable anion. Inone embodiment, the polymerizable cation comprises an aromatic moiety.The polymerizable anion is preferably a carboxylate anion such as anaromatic carboxylate anion.

Such polymerizable ionic liquids may comprise a substituted ammoniumcation. The polymerizable ionic liquid may have the general formula:

whereinR³ is independently hydrogen or a C2-C8 alkyl group;R² is an ethylenically unsaturated group;D is a divalent linking group comprising an aromatic moiety;a is 1-4;b is 0-3;a+b=4; andX⁻ is an organic cation comprising at least one ethylenicallyunsaturated group.

The ethylenically unsaturated group may be a vinyl group.

Some illustrative species include

In another favored embodiment, the polymerizable composition comprises apolymerizable ionic liquid comprising an aromatic carboxylate anion.

Such (e.g. free-radically) polymerizable ionic liquids may have thegeneral formula:

whereinX is nitrogen or phosphorus;R3 and R4 are independently alkyl or heteroalkyl, and at least one R3 orR4 comprises a free-radically polymerizable group;D comprises an aromatic moiety and optionally comprises a linking groupbetween the carboxylate end group and aromatic moiety and/or optionallycomprises a linking group between the aromatic moiety and R4; andb is 0-2.

The free-radically polymerizable groups are preferably (meth)acrylategroups. The aromatic moiety of D typically comprises one, two, or threearomatic rings that are optionally fused, such as in the case ofphthalate or aromatic rings derived from biphenyl or triphenylcompounds.

In some embodiments, both the substituted (e.g. ammonium) cation and thearomatic carboxylate anion each comprise at least one free radicallypolymerizable group, such as (meth)acrylate groups. In some embodiments,two R3 are alkyl groups and one R3 group comprises a (meth)acrylategroup. In another embodiment, two R3 are alkyl groups and one R3 groupcomprises an aromatic (e.g. phenyl) (meth)acrylate group. The alkylgroups of R3 typically comprise at least one carbon atom (e.g. methyl)and no greater than 8, or no greater than 6, or no greater than 4 carbonatoms. A linking group is typically present between the terminal (e.g.free-radically) polymerizable (meth)acrylate group and the (e.g.ammonium) cation (X⁺), a previously described. D may comprise a divalent(e.g. ester) linking group between a (e.g. phenyl) aromatic group andterminal (meth)acrylate group.

Examples of such free-radically polymerizable ionic liquids include:

In another favored embodiment, the composition comprises amonofunctional polymerizable ionic liquid comprising a non-polymerizablecation, such as a substituted imidazolium cation and a polymerizableanion. The imidazolium cation is typically substituted with one or twolower alkyl groups of 1 to 4 carbon atoms. The anion is preferably a(e.g. nonfluorinated) sulfonate anion. One favored species is

The species described herein can include various other anions, aspreviously described.

The polymerizable ionic liquids described herein can be made by severalmethods. One method includes reaction of a hydroxyl functional ionicprecursor with a polymerizable isocyanate such as depicted by thefollowing reaction scheme:

Commercially available starting materials includetris-(2-hydroxyethyl)-methyl ammonium methyl sulfate available from BASF(BASIONIC FS01), diethanolamine hydrochloride, 2-amino-1,3-propanediolhydrochloride, and tris(hydroxymethyl)aminomethane hydrochloride. Theionic product may be further reacted to exchange the anion using anionmetathesis as described in “Ionic Liquids”, Meindersma, G. W., Maase,M., and De Haan, A. B., Ullmann's Encyclopedia of Industrial Chemistry,2007.

Another method includes the reaction of a hydroxyl functional amineprecursor with a polymerizable isocyanate, followed by alkylation oracidification, such as depicted by the following reaction scheme:

Commercially available starting materials include diethanol amine,diisopropanol amine, N-methyldiethanol amine, N-ethyldiethanol amine,N-butyldiethanol amine, triethanol amine,1-[N,N-bis(2-hydroxyethyl)-amino]-2-propanol, triisopropanol amine,3-amino-1,2-propanediol, 3-(dimethylamino)-1,2-propanediol,3-(diethylamino)-1,2-propanediol, 3-(dipropylamino)-1,2-propanediol,3-(diisopropylamino)1,2,-propanediol, 2-amino-1,3-propanediol,2-amino-2-ethyl-1,3,-propanediol, 2-amino-2-methyl-1,3,-propanediol,tris(hydroxymethyl)amino methane,bis(2-hydroxyethyl)amino-tris(hydroxymethyl)methane,2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol, N,N′bis(2-hydroxyethyl)-ethylenediamine,N—N—N′—N′-tetrakis(2-hydroxypropyl)-ethylenediamine,1,3-bis[tris(hydroxymethyl)-methylamino]propane,3-pyrrolidino-1,2-propanediol, 3-piperidino-1,2-propanediol, and1,4-bis(2-hydroxyethyl)-piperazine.

Useful alkylating agents include alkyl halides, sulfates, andphosphonate esters, such as methyl iodide, ethyl iodide, methyl bromide,ethyl bromide, dimethyl sulfate, diethyl sulfate, and dimethylmethylphosphonate. Useful acidification agents include carboxylic acids,organosulfonic acids, and organophosphonic acids and inorganic acidssuch as hydrochloric acid, hydrofluoric acid, hydrobromic acid,phosphoric acid, nitric acid and the like.

Another method includes the reaction of an amine with an acrylatecompound to give a polymerizable amine precursor, followed by alkylationor acidification, such as depicted by the following reaction scheme:

Commercially available starting materials include amines such asmethylamine, ethylamine, propylamine, butylamine, hexylamine,isopropylamine, isobutylamine, 1-methylbutylamine, 1-ethyl propylamine,2-methylbutylamine, isoamylamine, 1,2-dimethylpropylamine,1,3-dimethylbutylamine, 3,3-dimethylbutylamine, 2-aminoheptane,3-aminoheptane, 1-methylheptyamine, 2-ethylhexylamine,1,5-dimethylhexylamine, cyclopropylamine, cyclohexylamine,cyclobutylamine, cyclopentylamine, cycloheptylamine, cyclooctylamine,2-aminonorbornane, 1-adamantanamine, allylamine,tetrahydrofurfurylamine, ethanolamine, 3-amino-1-propanol,2-(2-aminoethoxy)ethanol, benzylamine, phenethylamine,3-phenyl-1-propylamine, 1-aminoindan, ethylenediamine, diaminopropane,and hexamethylenediamine.

Another method, that provides a polymerizable ionic liquid containing anether linking group, includes the reaction of a hydroxyl functionalprecursor with a functionalized (meth)acrylate molecule such as depictedby the following reaction scheme:

Another method, that provides a polymerizable ionic liquid containing anamide linking group, includes the reaction of an amine functionalprecursor with a functionalized (meth)acrylate molecule such as depictedby the following reaction scheme:

Another illustrative method, that provides a polymerizable ionic liquidcontaining a urea linking group, is depicted by the following reactionscheme:

In addition to the (e.g. multifunctional) polymerizable ionic liquidsdescribed herein, the curable component of the composition can include awide variety of other ethylenically unsaturated compounds (with orwithout acid functionality), epoxy-functional (meth)acrylate resins,vinyl ethers, and the like.

The (e.g., photopolymerizable) compositions may include compounds havingfree radically reactive functional groups that may include monomers,oligomers, and polymers having one or more ethylenically unsaturatedgroup. Suitable compounds contain at least one ethylenically unsaturatedbond and are capable of undergoing addition polymerization. Examples ofuseful ethylenically unsaturated compounds include acrylic acid esters,methacrylic acid esters, hydroxy-functional acrylic acid esters,hydroxy-functional methacrylic acid esters, and combinations thereof.Such free radically polymerizable compounds include mono-, di- orpoly-(meth)acrylates (i.e., acrylates and methacrylates).

Some illustrative examples of other polymerizable monomers, oligomers,or polymers useful herein include, for example, poly(meth)acryl monomersand mono(meth)acryl monomers such as (a) mono(meth)acryl containingcompounds such as phenoxyethyl acrylate, ethoxylated phenoxyethylacrylate, 2-ethoxyethoxyethyl acrylate, ethoxylated tetrahydrofurfuralacrylate, and caprolactone acrylate, (b) di(meth)acryl containingcompounds such as 1,3-butylene glycol diacrylate, 1,4-butanedioldiacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol monoacrylatemonomethacrylate, ethylene glycol diacrylate, alkoxylated aliphaticdiacrylate, alkoxylated cyclohexane dimethanol diacrylate, alkoxylatedhexanediol diacrylate, alkoxylated neopentyl glycol diacrylate,caprolactone modified neopentylglycol hydroxypivalate diacrylate,caprolactone modified neopentylglycol hydroxypivalate diacrylate,cyclohexanedimethanol diacrylate, diethylene glycol diacrylate,dipropylene glycol diacrylate, ethoxylated (10) bisphenol A diacrylate,ethoxylated (3) bisphenol A diacrylate, ethoxylated (30) bisphenol Adiacrylate, ethoxylated (4) bisphenol A diacrylate, hydroxypivalaldehydemodified trimethylolpropane diacrylate, neopentyl glycol diacrylate,polyethylene glycol (200) diacrylate, polyethylene glycol (400)diacrylate, polyethylene glycol (600) diacrylate, propoxylated neopentylglycol diacrylate, tetraethylene glycol diacrylate,tricyclodecanedimethanol diacrylate, triethylene glycol diacrylate,tripropylene glycol diacrylate; (c) tri(meth)acryl containing compoundssuch as glycerol triacrylate, trimethylolpropane triacrylate,pentaerthyritol triacrylate, ethoxylated triacrylates (e.g., ethoxylated(3) trimethylolpropane triacrylate, ethoxylated (6) trimethylolpropanetriacrylate, ethoxylated (9) trimethylolpropane triacrylate, ethoxylated(20) trimethylolpropane triacrylate, propoxylated triacrylates (e.g.,propoxylated (3) glyceryl triacrylate, propoxylated (5.5) glyceryltriacrylate, propoxylated (3) trimethylolpropane triacrylate,propoxylated (6) trimethylolpropane triacrylate), trimethylolpropanetriacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate; (d) higherfunctionality (meth)acryl containing compounds such as pentaerythritoltetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritolpentaacrylate, ethoxylated (4) pentaerythritol tetraacrylate,caprolactone modified dipentaerythritol hexaacrylate; (e) oligomeric(meth)acryl compounds such as, for example, urethane acrylates,polyester acrylates, epoxy acrylates; polyacrylamide analogues of theforegoing; and combinations thereof. Such compounds are widely availablefrom vendors such as, for example, Sartomer Company of Exton, Pa.; UCBChemicals Corporation of Smyrna, Ga.; Cytec Corporation, Cognis, andAldrich Chemical Company of Milwaukee, Wis. Additional useful(meth)acrylate materials include hydantoin moiety-containingpoly(meth)acrylates, for example, as described in U.S. Pat. No.4,262,072 (Wendling et al.).

Other compounds that contain at least one ethylenically unsaturated bondinclude methyl(meth)acrylate, ethyl(meth)acrylate,isopropyl(meth)acrylate, n-hexyl (meth)acrylate, stearyl(meth)acrylate,allyl(meth)acrylate, 1,3-propanediol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, 1,2,4-butanetrioltri(meth)acrylate, 1,4-cyclohexanediol di(meth)acrylate, sorbitolhex(meth)acrylate, tetrahydrofurfuryl (meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, andtrishydroxyethyl-isocyanurate tri(meth)acrylate; (meth)acrylamides(i.e., acrylamides and methacrylamides) such as (meth)acrylamide,methylene bis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane(meth)acrylates; and vinyl compounds such as styrene, diallyl phthalate,divinyl succinate, divinyl adipate and divinyl phthalate. Other suitablefree radically polymerizable compounds include siloxane-functional(meth)acrylates. Mixtures of two or more free radically polymerizablecompounds can be used if desired.

The curable (e.g. dental) composition may also contain hydroxyl groupsand ethylenically unsaturated groups in a single molecule. Examples ofsuch materials include hydroxyalkyl(meth)acrylates, such as2-hydroxyethyl(meth)acrylate and 2-hydroxypropyl(meth)acrylate; glycerolmono- or di-(meth)acrylate; trimethylolpropane mono- ordi-(meth)acrylate; pentaerythritol mono-, di-, and tri-(meth)acrylate;sorbitol mono-, di-, tri-, tetra-, or penta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-ethacryloxypropoxy)phenyl]propane (bisGMA).Suitable ethylenically unsaturated compounds are also available from awide variety of commercial sources, such as Sigma-Aldrich, St. Louis.

In certain embodiments curable components can include PEGDMA(polyethyleneglycol dimethacrylate having a molecular weight ofapproximately 400), bisGMA, UDMA (urethane dimethacrylate), GDMA(glycerol dimethacrylate), TEGDMA (triethyleneglycol dimethacrylate),bisEMA6 as described in U.S. Pat. No. 6,030,606 (Holmes), and NPGDMA(neopentylglycol dimethacrylate).

An initiator is typically added to the multifunctional polymerizableionic liquid or to the mixture of polymerizable ingredients comprisingat least one multifunctional polymerizable ionic liquid, as describedherein. The initiator is sufficiently miscible with the resin system topermit ready dissolution in (and discourage separation from) thepolymerizable composition. Typically, the initiator is present in thecomposition in effective amounts, such as from about 0.1 weight percentto about 5.0 weight percent, based on the total weight of thecomposition.

In some embodiments, the multifunctional polymerizable ionic liquid orcomposition comprising such is photopolymerizable and the compositioncontains a photoinitiator (i.e., a photoinitiator system) that uponirradiation with actinic radiation initiates the polymerization (orhardening) of the composition. Such photopolymerizable compositions canbe free radically polymerizable. The photoinitiator typically has afunctional wavelength range from about 250 nm to about 800 nm.

Suitable photoinitiators (i.e., photoinitiator systems that include oneor more compounds) for polymerizing free radically photopolymerizablecompositions include binary and tertiary systems. Typical tertiaryphotoinitiators include an iodonium salt, a photosensitizer, and anelectron donor compound as described in U.S. Pat. No. 5,545,676(Palazzotto et al.). Iodonium salts include diaryl iodonium salts, e.g.,diphenyliodonium chloride, diphenyliodonium hexafluorophosphate, anddiphenyliodonium tetrafluoroboarate. Some preferred photosensitizers mayinclude monoketones and diketones (e.g. alpha diketones) that absorbsome light within a range of about 300 nm to about 800 nm (preferably,about 400 nm to about 500 nm) such as camphorquinone, benzil, furil,3,3,6,6-tetramethylcyclohexanedione, phenanthraquinone and other cyclicalpha diketones. Of these camphorquinone is typically preferred.Preferred electron donor compounds include substituted amines, e.g.,ethyl 4-(N,N-dimethylamino)benzoate. Other suitable photoinitiators forpolymerizing free radically photopolymerizable compositions include theclass of phosphine oxides that typically have a functional wavelengthrange of about 380 nm to about 1200 nm. Preferred phosphine oxide freeradical initiators with a functional wavelength range of about 380 nm toabout 450 nm are acyl and bisacyl phosphine oxides.

Commercially available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelength ranges of greaterthan about 380 nm to about 450 nm includebis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (IRGACURE 819, CibaSpecialty Chemicals, Tarrytown, N.Y.),bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (CGI403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE 1700, Ciba SpecialtyChemicals), a 1:1 mixture, by weight, ofbis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR 4265, Ciba SpecialtyChemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRINLR8893X, BASF Corp., Charlotte, N.C.).

Tertiary amine reducing agents may be used in combination with anacylphosphine oxide. Illustrative tertiary amines include ethyl4-(N,N-dimethylamino)benzoate and N,N-dimethylaminoethyl methacrylate.When present, the amine reducing agent is present in thephotopolymerizable composition in an amount from about 0.1 weightpercent to about 5.0 weight percent, based on the total weight of thecomposition.

In some preferred embodiments, the curable composition may be irradiatedwith ultraviolet (UV) rays. For this embodiment, suitablephotoinitiators are those available under the trade designationsIRGACURE and DAROCUR from Ciba Speciality Chemical Corp., Tarrytown,N.Y. and include 1-hydroxy cyclohexyl phenyl ketone (IRGACURE 184),2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651),bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide (IRGACURE 819),1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one(IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone(IRGACURE 369),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE907), and 2-hydroxy-2-methyl-1-phenyl propan-1-one (DAROCUR 1173).

The photopolymerizable compositions are typically prepared by admixingthe various components of the compositions. For embodiments wherein thephotopolymerizable compositions are not cured in the presence of air,the photoinitiator is combined under “safe light” conditions (i.e.,conditions that do not cause premature hardening of the composition).Suitable inert solvents may be employed if desired when preparing themixture. Examples of suitable solvents include acetone anddichloromethane.

Hardening is affected by exposing the composition to a radiation source,preferably an ultraviolet or visible light source. It is convenient toemploy light sources that emit actinic radiation light between 20 nm and800 nm such as quartz halogen lamps, tungsten-halogen lamps, mercuryarcs, carbon arcs, low-, medium-, and high-pressure mercury lamps,plasma arcs, light emitting diodes, and lasers. In general, useful lightsources have intensities in the range of 0.200-1000 W/cm². A variety ofconventional lights for hardening such compositions can be used.

The exposure may be accomplished in several ways. For example, thepolymerizable composition may be continuously exposed to radiationthroughout the entire hardening process (e.g., about 2 seconds to about60 seconds). It is also possible to expose the composition to a singledose of radiation, and then remove the radiation source, therebyallowing polymerization to occur. In some cases materials can besubjected to light sources that ramp from low intensity to highintensity. Where dual exposures are employed, the intensity of eachdosage may be the same or different. Similarly, the total energy of eachexposure may be the same or different.

The multifunctional polymerizable ionic liquid or compositionscomprising such may be chemically hardenable, i.e., the compositionscontain a chemical initiator (i.e., initiator system) that canpolymerize, cure, or otherwise harden the composition without dependenceon irradiation with actinic radiation. Such chemically hardenable (e.g.,polymerizable or curable) composition are sometimes referred to as“self-cure” compositions and may include redox cure systems, thermallycuring systems and combinations thereof. Further, the polymerizablecomposition may comprise a combination of different initiators, at leastone of which is suitable for initiating free radical polymerization.

The chemically hardenable compositions may include redox cure systemsthat include a polymerizable component (e.g., an ethylenicallyunsaturated polymerizable component) and redox agents that include anoxidizing agent and a reducing agent.

The reducing and oxidizing agents react with or otherwise cooperate withone another to produce free-radicals capable of initiatingpolymerization of the resin system (e.g., the ethylenically unsaturatedcomponent). This type of cure is a dark reaction, that is, it is notdependent on the presence of light and can proceed in the absence oflight. The reducing and oxidizing agents are preferably sufficientlyshelf-stable and free of undesirable colorization to permit theirstorage and use under typical conditions.

Useful reducing agents include ascorbic acid, ascorbic acid derivatives,and metal complexed ascorbic acid compounds as described in U.S. Pat.No. 5,501,727 (Wang et al.); amines, especially tertiary amines, such as4-tert-butyl dimethylaniline; aromatic sulfinic salts, such asp-toluenesulfinic salts and benzenesulfinic salts; thioureas, such as1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea,1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixtures thereof.Other secondary reducing agents may include cobalt (II) chloride,ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (dependingon the choice of oxidizing agent), salts of a dithionite or sulfiteanion, and mixtures thereof. Preferably, the reducing agent is an amine.

Suitable oxidizing agents will also be familiar to those skilled in theart, and include but are not limited to persulfuric acid and saltsthereof, such as sodium, potassium, ammonium, cesium, and alkyl ammoniumsalts. Additional oxidizing agents include peroxides such as benzoylperoxides, hydroperoxides such as cumyl hydroperoxide, t-butylhydroperoxide, and amyl hydroperoxide, as well as salts of transitionmetals such as cobalt (III) chloride and ferric chloride, cerium (IV)sulfate, perboric acid and salts thereof, permanganic acid and saltsthereof, perphosphoric acid and salts thereof, and mixtures thereof.

It may be desirable to use more than one oxidizing agent or more thanone reducing agent. Small quantities of transition metal compounds mayalso be added to accelerate the rate of redox cure. The reducing oroxidizing agents can be microencapsulated as described in U.S. Pat. No.5,154,762 (Mitra et al.). This will generally enhance shelf stability ofthe polymerizable composition, and if necessary permit packaging thereducing and oxidizing agents together. For example, through appropriateselection of an encapsulant, the oxidizing and reducing agents can becombined with an acid-functional component and optional filler and keptin a storage-stable state.

The compositions can also be cured with a thermally or heat activatedfree radical initiator. Typical thermal initiators include peroxidessuch as benzoyl peroxide and azo compounds such asazobisisobutyronitrile.

In some embodiments, such as when the composition comprises appreciableamounts of (e.g. nanoparticle) filler. Such compositions preferablyinclude at least 40 wt-%, more preferably at least 45 wt-%, and mostpreferably at least 50 wt-% filler, based on the total weight of thecomposition. In some embodiments the total amount of filler is at most90 wt-%, preferably at most 80 wt-%, and more preferably at most 75 wt-%filler.

In such compositions comprising appreciable amounts of filler, the oneor more multifunctional polymerizable ionic liquids are typicallypresent in an amount totaling at least 5 wt-%, 6 wt-%, 7 wt-%, 8 wt-%, 9wt-%, or 10 wt-%, based on the total weight of the composition. Theconcentration of multifunctional polymerizable ionic liquids isgenerally no greater than about 60 wt-%. In some embodiments the totalamount of multifunctional polymerizable ionic liquids is at most 40wt-%, preferably at most 30 wt-%, and more preferably at most 25 wt-%.

Compositions suitable for use as adhesives can also include filler inamount of at least 1 wt-%, 2 wt-%, 3 wt-%, 4 wt-%, or 5 wt-% based onthe total weight of the composition. For such embodiments, the totalconcentration of filler is at most 40 wt-%, preferably at most 20 wt-%,and more preferably at most 15 wt-% filler, based on the total weight ofthe composition.

Fillers may be selected from one or more of a wide variety of materials,as known in the art.

The filler can be an inorganic material. It can also be a crosslinkedorganic material that is insoluble in the polymerizable resin, and isoptionally filled with inorganic filler. The filler can be radiopaque,radiolucent, or nonradiopaque. Fillers can be ceramic in nature.

Inorganic filler particles include quartz (i.e., silica), submicronsilica, zirconia, submicron zirconia, and non-vitreous microparticles ofthe type described in U.S. Pat. No. 4,503,169 (Randklev).

Filler components include nanosized silica particles, nanosized metaloxide particles, and combinations thereof. Nanofillers are alsodescribed in U.S. Pat. Nos. 7,090,721 (Craig et al.), 7,090,722 (Budd etal.), 7,156,911 (Kangas et al.), and 7,649,029 (Kolb et al.).

Examples of suitable organic filler particles include filled or unfilledpulverized polycarbonates, polyepoxides, poly(meth)acrylates and thelike. Commonly employed filler particles are quartz, submicron silica,and non-vitreous microparticles of the type described in U.S. Pat. No.4,503,169 (Randklev).

Mixtures of these fillers can also be used, as well as combinationfillers made from organic and inorganic materials.

Fillers may be either particulate or fibrous in nature. Particulatefillers may generally be defined as having a length to width ratio, oraspect ratio, of 20:1 or less, and more commonly 10:1 or less. Fiberscan be defined as having aspect ratios greater than 20:1, or morecommonly greater than 100:1. The shape of the particles can vary,ranging from spherical to ellipsoidal, or more planar such as flakes ordiscs. The macroscopic properties can be highly dependent on the shapeof the filler particles, in particular the uniformity of the shape.

Micron-size particles are very effective for improving post-cure wearproperties. In contrast, nanoscopic fillers are commonly used asviscosity and thixotropy modifiers. Due to their small size, highsurface area, and associated hydrogen bonding, these materials are knownto assemble into aggregated networks.

In some embodiments, the composition preferably comprise a nanoscopicparticulate filler (i.e., a filler that comprises nanoparticles) havingan average primary particle size of less than about 0.100 micrometers(i.e., microns), and more preferably less than 0.075 microns. As usedherein, the term “primary particle size” refers to the size of anon-associated single particle. The average primary particle size can bedetermined by cutting a thin sample of hardened composition andmeasuring the particle diameter of about 50-100 particles using atransmission electron micrograph at a magnification of 300,000 andcalculating the average. The filler can have a unimodal or polymodal(e.g., bimodal) particle size distribution. The nanoscopic particulatematerial typically has an average primary particle size of at leastabout 2 nanometers (nm), and preferably at least about 7 nm. Preferably,the nanoscopic particulate material has an average primary particle sizeof no greater than about 50 nm, and more preferably no greater thanabout 20 nm in size. The average surface area of such a filler ispreferably at least about 20 square meters per gram (m²/g), morepreferably, at least about 50 m²/g, and most preferably, at least about100 m²/g.

In some preferred embodiments, the composition comprises silicananoparticles. Suitable nano-sized silicas are commercially availablefrom Nalco Chemical Co. (Naperville, Ill.) under the product designationNALCO COLLOIDAL SILICAS. For example, preferred silica particles can beobtained from using NALCO products 1040, 1042, 1050, 1060, 2327 and2329.

Silica particles are preferably made from an aqueous colloidaldispersion of silica (i.e., a sol or aquasol). The colloidal silica istypically in the concentration of about 1 to 50 weight percent in thesilica sol. Colloidal silica sols that can be used are availablecommercially having different colloid sizes, see Surface & ColloidScience, Vol. 6, ed. Matijevic, E., Wiley Interscience, 1973. Preferredsilica sols are supplied as a dispersion of amorphous silica in anaqueous medium (such as the Nalco colloidal silicas made by NalcoChemical Company) and those which are low in sodium concentration andcan be acidified by admixture with a suitable acid (e.g. Ludox colloidalsilica made by E. I. Dupont de Nemours & Co. or Nalco 2326 from NalcoChemical Co.).

Preferably, the silica particles in the sol have an average particlediameter of about 5-100 nm, more preferably 10-50 nm, and mostpreferably 12-40 nm. A particularly preferred silica sol is NALCO 1041.

In some embodiments, the composition comprises zirconia nanoparticles.Suitable nano-sized zirconia nanoparticles can be prepared usinghydrothermal technology as described in U.S. Pat. No. 7,241,437(Davidson et al.).

In some embodiments, lower refractive index (e.g. silica) nanoparticlesare employed in combination with high refractive index (e.g. zirconia)nanoparticles in order to index match (refractive index within 0.02) thefiller to the refractive index of the polymerizable resin.

In some embodiments, the nanoparticles are in the form of nanoclusters,i.e. a group of two or more particles associated by relatively weakintermolecular forces that cause the particles to clump together, evenwhen dispersed in the resin.

Preferred nanoclusters can comprise a substantially amorphous cluster ofnon-heavy (e.g. silica) particles, and amorphous heavy metal oxide (i.e.having an atomic number greater than 28) particles such as zirconia. Theparticles of the nanocluster preferably have an average diameter of lessthan about 100 nm. Suitable nanocluster fillers are described in U.S.Pat. No. 6,730,156 (Windisch et al.); incorporated herein by reference.

In some preferred embodiments, the composition comprises nanoparticlesand/or nanoclusters surface treated with an organometallic couplingagent to enhance the bond between the filler and the resin. Theorganometallic coupling agent may be functionalized with reactive curinggroups, such as acrylates, methacrylates, vinyl groups and the like.

Suitable copolymerizable organometallic compounds may have the generalformulas: CH₂═C(CH₃)_(m)Si(OR)_(n) or CH₂═C(CH₃)_(m)C═OOASi(OR)_(n);wherein m is 0 or 1, R is an alkyl group having 1 to 4 carbon atoms, Ais a divalent organic linking group, and n is from 1 to 3. Preferredcoupling agents include gamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like.

In some embodiments, a combination of surface modifying agents can beuseful, wherein at least one of the agents has a functional groupco-polymerizable with a hardenable resin. Other surface modifying agentswhich do not generally react with hardenable resins can be included toenhance dispersibility or rheological properties. Examples of silanes ofthis type include, for example, aryl polyethers, alkyl, hydroxy alkyl,hydroxy aryl, or amino alkyl functional silanes.

The surface modification can be done either subsequent to mixing withthe monomers or after mixing. It is typically preferred to combine theorganosilane surface treatment compounds with nanoparticles beforeincorporation into the resin. The required amount of surface modifier isdependant upon several factors such as particle size, particle type,modifier molecular wt, and modifier type. In general it is preferredthat approximately a monolayer of modifier is attached to the surface ofthe particle.

The surface modified nanoparticles can be substantially fully condensed.Fully condensed nanoparticles (with the exception of silica) typicallyhave a degree of crystallinity (measured as isolated metal oxideparticles) greater than 55%, preferably greater than 60%, and morepreferably greater than 70%. For example, the degree of crystallinitycan range up to about 86% or greater. The degree of crystallinity can bedetermined by X-ray diffraction techniques. Condensed crystalline (e.g.zirconia) nanoparticles have a high refractive index whereas amorphousnanoparticles typically have a lower refractive index.

Optionally, compositions may contain solvents (e.g., alcohols (e.g.,propanol, ethanol), ketones (e.g., acetone, methyl ethyl ketone), esters(e.g., ethyl acetate), other nonaqueous solvents (e.g.,dimethylformamide, dimethylacetamide, dimethylsulfoxide,1-methyl-2-pyrrolidinone)), and water.

If desired, the compositions can contain additives such as indicators,dyes, pigments, inhibitors, accelerators, viscosity modifiers, wettingagents, buffering agents, radical and cationic stabilizers (for exampleBHT,), and other similar ingredients that will be apparent to thoseskilled in the art. The curable composition may comprises various otherethylenically unsaturated monomer(s), oligomer(s), and polymer(s) andadditive as known in the art, such as described in U.S. ProvisionalApplication Ser. No. 61/289,098 titled “CURABLE DENTAL COMPOSITIONS ANDARTICLES COMPRISING POLYMERIZABLE IONIC LIQUIDS”; incorporated herein byreference.

The present invention will be further illustrated with reference tovarious dental compositions including dental adhesives as illustrativeadhesives; dental sealants as illustrative coatings; and dentalcomposites as illustrative articles having high mechanical strength.Articles, such as dental composites, can be made from the curablecomposition described herein by casting the curable composition incontact with a mold and curing the composition. Articles, such as dentalcomposites, can alternatively be made by first curing the compositionand then mechanically milling the composition into the desired article.

The curable blends of polymerizable ionic liquid in combination withconvention (e.g. (meth)acrylate) ethylenically unsaturated monomers canbe used for a variety of other uses, particularly (e.g. photo) curablecoatings. A coated article can be prepared by applying the compositiondescribed herein to a substrate and curing the composition.

The curable blends can be applied to a variety of substrates. Suitablesubstrate materials include inorganic substrates such as glass orceramics, natural and synthetic organic substrates such as paper, wood,as well as thermosetting or thermoplastic polymers such aspolycarbonate, poly(meth)acrylate (e.g., polymethyl methacrylate or“PMMA”), polyolefins (e.g., polypropylene or “PP”), polyurethane,polyesters (e.g., polyethylene terephthalate or “PET”), polyamides,polyimides, phenolic resins, cellulose diacetate, cellulose triacetate,polystyrene, styrene-acrylonitrile copolymers, epoxies, and the like.The substrate thickness typically also will depend on the intended use.For most applications, substrate thicknesses of less than about 0.5 mmare preferred, and more preferably about 0.02 to about 0.2 mm. Thesubstrate can be treated to improve adhesion between the substrate andcurable coating compositions, e.g., chemical treatment, corona treatmentsuch as air or nitrogen corona, plasma, flame, or actinic radiation. Ifdesired, an optional tie layer or (e.g. polymerizable ionic liquidbased) primer can be applied to the substrate to increase the interlayeradhesion.

The curable coating composition can be applied using a variety ofconventional coating methods. Suitable coating methods include, forexample, spin coating, knife coating, die coating, wire coating, floodcoating, padding, spraying, roll coating, dipping, brushing, foamapplication, and the like. The coating is dried, typically using aforced air oven. The dried coating is at least partially and typicallycompletely cured using an energy source.

Objects and advantages are further illustrated by the followingexamples, but the particular materials and amounts thereof recited inthese examples, as well as other conditions and details, should not beconstrued to unduly limit this invention. Unless otherwise indicated,all parts and percentages are on a weight basis.

EXAMPLES

Abbreviation Chemical Description (Supplier, Location) PolymerizableMonomer BisGMA 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane Bis EMA6 ethoxylated bisphenol Amethacrylate as further described in U.S. Pat. No. 6,030,606 availablefrom Sartomer as “CD541” TEGDMA triethyleneglycol dimethacrylate HEMA2-Hydroxyethyl methacrylate (Sigma-Aldrich, St. Louis, MO) UDMADiurethane dimethacrylate (CAS No. 41137-60-4), commercially availableas Rohamere 6661-0 (Rohm Tech, Inc., Malden, MA) Inorganic Fillers S/TTiO₂ filler Silane treated TiO₂ filler: The pH of an acetic acid watersolution was adjusted to slightly less than 2.0 by adding 1.47 parts ofacetic acid into 1.47 parts of DI water at room temperature. Thissolution was slowly added to 4.37 parts of methacryloxypropyltrimethoxysilane (available from GE Silicones under the trade designation“Silquest A-174”) and 4.37 parts of methanol solution with stirring,stirring the solution for one hour. To this solution was added 96 partsof Ti Pure R-960 Titanium Dioxide from Dupont and 1.71 parts of AerosilR-972 from Degussa, and mixed vigorously for about 10 minutes. Themixture was dried at 115° C. for 4 hours, crushed, and screened througha 74 micron nylon screen. R812S Filler Hydrophobic fumed silicaavailable from Degussa Evonik Industries, Parsippany, NJ, under thetrade designation “Aerosil Fumed Silica R812S”. Zr/Si Filler One hundredparts zirconia silica filler of average particle size 0.6-0.9micrometers was mixed with deionized water at a solution temperature ofbetween 20-30° C., and the pH is adjusted to 3-3.3 with trifluoroaceticacid (0.278 parts). The A- 174 silane was added to the slurry in anamount 7 parts, and the blend was mixed over 2 hours. At the end of 2hours, the pH is neutralized with calcium hydroxide. The filler isdried, crushed and screened through a 74 or 100 micron screen. Zr/SiNano- Refers to silane-treated zirconia/silica nanocluster fillerCluster Filler prepared essentially as described in U.S. Pat. No.6,730,156 (Preparatory Example A (line 51-64) and Example B (column 25line 65 through column 26 line 40). 20 nm Si Refers to silane-treatednano-sized silica having a nominal Nanomer particle size ofapproximately 20 nanometers, prepared Filler essentially as described inU.S. Pat. No. 6,572,693 B1, (column 21, lines 63-67 for Nanosizedparticle filler, Type #2. Components of Photointiator Package BHT2,6-di-tert-butyl-4-methylphenol (Sigma-Aldrich Fine Chemicals, St.Louis, MO) CPQ camphorquinone (Sigma-Aldrich) DPIHFP “DPIHFP” refers todiphenyl iodonium hexafluorophosphate; EDMAB ethyl4-(N,N-dimethylamino)benzoate (Sigma-Aldrich)

Synthesis of Polymerizable Ionic Liquids Preparation of “PIL A”—Prep 1

Butyl imidazole (4.82 g, 0.04 mol), BHT (0.015 g), and methanol (50 mL)were mixed with in a flask equipped with magnetic stirring.2-acrylamido-2-methyl-1-propanesulfonic acid (8.05 g, 0.04 mol) andmethanol (50 mL) were added at room temperature. The acid dissolvedcompletely in 30 minutes. The reaction was stirred at room temperatureovernight. The solvent was then removed under vacuum to give a viscousliquid.

Preparation of “PIL A-1”—Prep 2

1-butyl-3-methylimidazolium hydrogen carbonate (Aldrich, 50% solution inmethanol:water (2:3), 16 g, 0.04 mol), BHT (0.010 g), and methanol (20mL) were mixed in a flask equipped with magnetic stirring.2-acrylamido-2-methyl-1-propanesulfonic acid (8.28 g, 0.04 mol) andmethanol (60 mL) were added while cooling the flash with a roomtemperature water bath. Carbon dioxide was generated and the mixturebecame clear. The reaction was stirred at room temperature for 4 hours.The solvent methanol and water was removed under vacuum to give aviscous liquid.

Preparation of PIL B

A mixture of n-butylamine (0.993 g, 14 mmol, Aldrich) andmethacryloxyethyl acrylate (5.00 g, 27 mmol, prepared according to Klee,J. E., et. al., Macromol. Chem. Phys., 200, 1999, 517) was stirred atroom temperature for 24 hours. The intermediate product was a colorlessliquid.

Dimethyl sulfate (0.57 g, 4.5 mmol) was added to the intermediateproduct from above (2.00 g, 4.5 mmol) dropwise over 10 minutes. Themixture was stirred for 17 hours to give the final PIL product as athick liquid.

Preparation of PIL-C (“POS-2”)

Polymerizable Onium Salt 2 (POS-2): represented by the followingformula:

To a solution of tris-(2-hydroxyethyl)methylammonium methylsulfate(11.58 g, 0.04 mol, available from BASF), isocyanatoethyl methacrylate(19.58 g, 0.12 mol), and 2,6-di-tert-butyl-4-methylphenol (BHT, 0.020 g,available from Aldrich) in methylene chloride (50 mL) in a flask fittedwith a drying tube and a magnetic stirrer was added a drop of dibutyltindilaurate. The solution was cooled in an ice bath and stirred for 3hours, then allowed to warm to room temperature and stirring wascontinued for another 36 hours. Progress of the reaction was monitoredby infrared spectroscopy, observing the disappearance of the isocyanateabsorption. When reaction was complete the solvent was removed atreduced pressure yielding a very viscous liquid.

Preparation of PIL D

To a stirred, ice cooled solution of tris-(2-hydroxyethyl)methylammoniummethylsulfate (17.38 g, 0.06 mol), mono-2-(methacryloyloxy)ethylsuccinate (41.42 g, 0.18 mol, available from Aldrich), and4-dimethylaminopyridine (1.098 g, 0.009 mol, available from Aldrich) inethyl acetate (150 mL) was added dropwise over a 2 hour period asolution of 1,3-dicyclohexylcarbodiimide (DCC, 37.1 g, 0.18 mol,available from Aldrich) in ethyl acetate (150 mL). After the DCCsolution was added, the temperature of the reaction mixture was allowedto rise gradually to room temperature, and then the reaction was stirredfor 14 hours. Then 0.5 g of deionized water and 2.0 g of silica gel wereadded into the flask and the reaction mixture stirred for 1 hour. Themixture was then filtered and solvent removed from the filtrate atreduced pressure to yield a very viscous liquid product having a slightyellow color.

Preparation of PIL E

Into a vial was placed 1.000 g (6.2 mmol) of N,N-dimethyl vinylbenzylamine (mixture of isomers, Aldrich) and 1.428 g (6.2 mmol)mono-(methacryloxy)ethyl succinate (Aldrich). After mixing for 5 minutesthe liquid product was obtained.

Preparation of PIL F

Into a vial was placed 1.000 g (6.2 mmol) of N,N-dimethyl vinylbenzylamine (mixture of isomers, Aldrich) and 1.726 g (6.2 mmol)mono-(methacryloxy)ethyl phthalate (Aldrich). After mixing for 5 minutesa liquid product was obtained.

Preparation of PIL G

A mixture of dimethylaminoethyl methacrylate (56.62 g, 0.36 mol),Prostab 5198 (17 mg), and mono-2-(methacryloxy)ethyl phthalate (Aldrich,100.00 g, 0.36 mol) was placed in a jar. The jar was capped and rolledat room temperature for 17 hours. A colorless oil was obtained.

Preparation of PIL H

A mixture of dimethylaminoethyl acrylate (51.47 g, 0.36 mol), Prostab5198 (17 mg), and mono-2-(methacryloxy)ethyl phthalate (100.00 g, 0.36mol) was placed in a jar. The jar was capped and rolled at roomtemperature for 17 hours. A colorless oil was obtained.

Preparation of PIL I

N-(3-aminopropyl)imidazole (Alfa Aesar, 2.55 g, 0.02 mol) andtetrahydrofuran (Alfa Aesar, 30 mL) were placed an a flask with magneticstirring. 2-Isocyanatoethyl methacrylate (Showa Denko, Japan, 3.26 g,0.02 mol) was added dropwise over 30 minutes while cooling the flask inan ice water bath. After three hours, mono-2-(methacryloxy)ethylphthalate (5.67 g, 0.02 mol) and tetrahydrofuran (10 mL) were added andthe mixture was stirred for three hours at room temperature. The solventwas removed under vacuum to give thick liquid product.

Determination of Air to Nitrogen Curing Exotherm Ratio:

The photo polymerization behavior of monomers under N2 and air wasexamined using differential scanning photocalorimetry (photo DSC). Thephoto DSC was a TA instrument (New Castle, Del.) with DSC module 2920.The light source was a mercury/argon lamp with an Oriel PN 59480 425 nmlong pass light filter. The light intensity was 3 mW/cm², measured usingan International Light light meter Model IL 1400 equipped with a ModelXRL, 340A detector. The photo curable samples contained 0.5%camphorquinone (Sigma-Aldrich), 1.0% ethyl 4-(N,N-dimethylamino)benzoate(Sigma-Aldrich) and 1.0% diphenyl iodium hexafluorophosphate as thephotoinitiator package. A 10 mg cured sample was used as a reference.

About 10 mg of the sample was weighed accurately for the testing with aHermetic Pan (aluminum sample pan) as the sample holder. The sampleswere equilibrated at 37° C. for 5 minutes, and then the light aperturewas opened to irradiate the sample. During irradiation the sampletemperature was held at 37° C. The total irradiation time was 30minutes. After 30 minutes, the aperture was closed and the samplemaintained at 37° C. for another 5 minutes. The samples were testedunder nitrogen and air atmosphere respectively.

The data was collected as heat output per unit weight (mW/g). The datawas analyzed using TA Thermal Solutions Universal Analysis software.

Monomers were run once under nitrogen, then an identical sample was rununder air. The DSC recorded the heat generation from the curing sampleduring exposure, and the area under the curve was integrated to givetotal Joules/gram of the monomer. The heat generated when the sample wascured in air was divided by the heat generated when the sample was curedin nitrogen to give the curing ratio. A higher ratio represents lessoxygen inhibition.

Testing Results for Photocuring a Monofunctional PIL and 2-HydroxyethylMethacrylate (HEMA, Available from Aldrich) by Photo DSC

Curing ratio (air/N2) 90 wt % PIL-A/10 wt % HEMA 0.90 80 wt % PIL-A/20wt % HEMA 0.89 70 wt % PIL-A/30 wt % HEMA 0.87 60 wt % PIL-A/40 wt %HEMA 0.88 50 wt % PIL-A/50 wt % HEMA 0.84 40 wt % PIL-A/60 wt % HEMA0.58 30 wt % PIL-A/70 wt % HEMA 0.46 20 wt % PIL-A/80 wt % HEMA 0.35 10wt % PIL-A/90 wt % HEMA 0.25Testing Results for Photocuring a Multifunctional PIL and TriethyleneGlycol Dimethacrylate (TEGDMA, Available from Aldrich) by Photo DSC

Curing ratio (air/N2) 100 wt % PIL-C 0.97 90 wt % PIL-C/10 wt % TEGDMA0.95 80 wt % PIL-C/20 wt % TEGDMA 0.93 70 wt % PIL-C/30 wt % TEGDMA 0.9460 wt % PIL-C/40 wt % TEGDMA 0.90 50 wt % PIL-C/50 wt % TEGDMA 0.84 40wt % PIL-C/60 wt % TEGDMA 0.79 30 wt % PIL-C/70 wt % TEGDMA 0.78 20 wt %PIL-C/80 wt % TEGDMA 0.60 10 wt % PIL-C/90 wt % TEGDMA 0.40 100 wt %TEGDMA 0.36

Testing Results for Photocuring a Multifunctional PIL Comprising aPolymerizable Cation and Polymerizable Anion by Photo DSC

Curing ratio (air/N2) 100 wt % PIL-E 0.79 100 wt % PIL-F 0.94 100 wt %PIL-G 0.97 100 wt % PIL-H 1.00 100 wt % PIL-I 0.98

Test Method for Evaluating Bond Strength of Dental Adhesive and DentalSealant to Dental Hard Tissues

Potted bovine teeth were ground using 120 grit sand paper to exposeenamel or dentin, then teeth were further polished using 320 grit sandpaper to smooth the surface. The bovine tooth surface was dried byapplying a stream of compressed air for 3 seconds, then a drop of primerwas applied, scrubbed for 20 seconds, dried by a stream of compressedair for 20 seconds, followed by application of a thin layer of adhesive(the adhesive composition is described below) with scrubbing for 20seconds. The primer and adhesive combination was then cured for 20seconds with a dental blue curing (3M ESPE Elipar Freelight 2) for 20seconds. Previously prepared molds made from a 2.5-mm thick “Teflon”sheet with a 4.7 mm diameter hole through the sheet were clamped to eachprepared tooth so that the central axis of the hole in the mold wasnormal to the tooth surface. The hole in each mold was filled with avisible light-curable dental restorative (available from 3M ESPE as“Filtek™ Z250 Restorative” A2 shade) and cured for 20 secondsirradiation with the dental curing light. The teeth and molds wereallowed to stand for about 5 minutes at room temperature, then stored indistilled water at 37° C. for 24 hours unless otherwise noted. The moldswere then carefully removed from the teeth, leaving a molded button ofrestorative attached to each tooth.

The adhesive strength was evaluated utilizing the wire loop method bymounting the acrylic disk in a holder clamped in the jaws of an “Instron1123” apparatus with the polished tooth surface oriented parallel to thedirection of pull. A loop of orthodontic wire (0.44 mm diameter) wasplaced around the restorative button adjacent to the polished toothsurface. The ends of the orthodontic wire were clamped in the pullingjaw of the Instron apparatus, thereby placing the bond in shear stress.The bond was stressed until it (or the dentin or button) failed using acrosshead speed of 2 mm/min. Five adhesion samples were prepared foreach set of primer and adhesive.

Control Primer A

Component Wt-% Maleic Acid 10 HEMA 45 Water 45 Total 100.0

Dental Primer B

Component Wt-% Maleic Acid 10 PIL A - Prep 1 45 Water 45 Total 100.0

Example 1 Dental Adhesive

Component Wt-% Solids Weight, g PIL-C 68.3 1.4 HEMA 0.0 0 TEGDMA 29.30.6 CPQ 0.5 0.01 EDMAB 1.0 0.02 DPIHFP 1.0 0.02 total 100 2.05

The test results of utilizing a conventional dental primer (ControlPrimer A), without a polymerizable ionic liquid in combination with adental adhesive (Example 1), comprising a polymerizable ionic liquidwere as follows:

Enamel Bond Std. Dentin Bond Std. Strength (MPa) Dev. Strength (MPa)Dev. Control Dental 11.6 4.3 10.9 2.3 Adhesive Example 1 14.3 3.9 13.93.1

Example 2 Dental Adhesive

Component Wt-% Solids Weight, g PIL C 9.8 0.2 HEMA 0.00 0 TEGDMA 87.81.8 CPQ 0.5 0.01 EDMAB 1.0 0.02 DPIHFP 1.0 0.02 Total 100 2.05

Using Dental Primer B as the primer, the dental adhesive of Example 2,(i.e. containing PIL C) was evaluated in the same manner as previouslydescribed and compared to the Control Dental Adhesive.

Enamel Bond Std. Dentin Bond Std. Strength (MPa) Dev. Strength (MPa)Dev. Example 2 18.6 3 21.2 1.2 Control Dental 15.8 5.8 13.4 2.1 Adhesive

The results show that the highest bond strength was achieved with apolymerizable ionic liquid based primer in combination with apolymerizable ionic liquid based adhesive.

Control Dental Sealant

Component Wt-% Solids Weight, g BisGMA 46.35 2.00 TEGDMA 46.35 2.00 CPQ0.23 0.01 EDMAB 1.16 0.05 DPIHFP 0.58 0.025 S/T TiO2 0.70 0.03 FillerR812S Filler 4.63 0.20 Total 100 4.32

Example 3 Dental Sealant

Component Wt-% Solids Weight, g PIL C 74.16 3.2 TEGDMA 18.54 0.8 CPQ0.23 0.01 EDMAB 1.16 0.05 DPIHFP 0.58 0.025 S/T TiO2 0.70 0.03 FillerR812S Filler 4.63 0.20 Total 100 4.32

Example 4 Dental Sealant

Component Wt-% Solids Weight, g PIL D 74.16 3.2 TEGDMA 18.54 0.8 CPQ0.23 0.01 EDMAB 1.16 0.05 DPIHFP 0.58 0.025 S/T TiO2 0.70 0.03 FillerR812S Filler 4.63 0.20 Total 100 4.32 Enamel Bond Std. Curing ratioStrength (MPa) Dev. (air/nitrogen) Example 3 16.0 2.9 0.96 Example 415.2 1.1 0.88 Control Sealant 13.2 2.8 0.71

Test Methods for Evaluating Composite: Watts Shrinkage Test Method

The Watts Shrinkage (Watts) Test Method measures shrinkage of a testsample in terms of volumetric change after curing. The samplepreparation (90-mg uncured composite test sample) and test procedurewere carried out as described in the following reference: Determinationof Polymerization Shrinkage Kinetics in Visible-Light-Cured Materials:Methods Development, Dental Materials, October 1991, pages 281-286.Results in terms of percent shrinkage were reported as the average ofthree replicates for each sample.

Barcol Hardness Test Method

Barcol Hardness of a test sample was determined according to thefollowing procedure. An uncured composite sample was cured in 2.5-mmthick TEFLON mold sandwiched between a sheet of polyester (PET) film anda glass slide for 30 seconds and cured with an ELIPAR Freelight 2 dentalcuring light (3M Company). After irradiation, the PET film was removedand the hardness of the sample at both the top and the bottom of themold was measured using a Barber-Coleman Impressor (a hand-held portablehardness tester; Model GYZJ 934-1; Barber-Coleman Company, IndustrialInstruments Division, Lovas Park, Ind.) equipped with an indenter. Topand bottom Barcol Hardness values were measured at 5 minutes after lightexposure. Results were reported as the average of three measurements.

Diametral Tensile Strength (DTS) Test Method DTS of a test sample wasprepared according to the following procedure. An uncured sample wasinjected into a 4-mm (inside diameter) glass tube that was capped withsilicone rubber plugs; and then the tube was compressed axially atapproximately 2.88 kg/cm² pressure for 5 minutes. The sample was thenlight cured for 80 seconds by exposure to a XL 1500 dental curing light(3M Company, St. Paul, Minn.), followed by irradiation for 90 seconds ina Kulzer UniXS curing box (Heraeus Kulzer GmbH, Germany). Cured sampleswere allowed to stand for 1 hour at about 37° C./90%+Relative Humidityand then were cut with a diamond saw to form 8-mm long cylindrical plugsfor measurement of compressive strength. The plugs were stored indistilled water at 37° C. for about 24 hours prior to testing.Measurements were carried out on an Instron tester (Instron 4505,Instron Corp., Canton, Mass.) with a 10 kilonewton (kN) load cell at acrosshead speed of 1 mm/minute according to ISO Specification 7489 (orAmerican Dental Association (ADA) Specification No. 27). Five cylindersof cured samples were prepared and measured with the results reported inMPa as the average of the five measurements.

For each of the following experiments, the Control Dental Composite wasa commercially available dental material available from 3M ESPE underthe trade designation “Filtek™ Z250 Restorative”.

Example 5 Dental Composite

Wt-% Total Composition Wt-% of Resin Weight - grams Part A—ResinComponent PIL C 12.636 63.18 3.1590 UDMA 4 20 1.0000 TEGDMA 3 15 0.7500CPQ 0.034 0.17 0.0085 EDMAB 0.2 1 0.0500 DPIHFP 0.1 0.5 0.0250 BHT 0.030.15 0.0075 Part B 80 NA 20 Zr/Si filler Total 100 100 25

The methacrylates monomers, polymerizable ionic liquids C,photoinitiator, and BHT were mixed in a medium cup. Zr/Si filler (13 g)was added and mixed for 3 minutes at a mixing speed of 3500 rpm. Themixture was allowed to cool down and an additional 5.0 g of Zr/Si fillerwas added and mixed at 3500 rpm for 1.5 minutes. The mixture was allowedto cool down again and then 1 g of Zr/Si filler was added and mixed at3500 rpm for 1.5 minutes. After cooling, 1.0 g of Zr/Si filler was addedand speed mixed at 3500 rpm for 1.5 minutes. After cooling, it was speedmixed further for 1.5 minutes to give the final paste.

DTS Std. Shrink- Std. Hard- Std. Curing ratio (MPa) Dev. age (%) Dev.ness Dev. (air/nitrogen) Example 5 90.2 8.8 2.3 0.03 82.7 0.6 0.99Control 90.9 10.4 2.1 0.05 83.5 1.4 0.85 Dental Composite

Example 6 Dental Composite

Wt-% Total Composition Wt-% Resin Weight grams Part A—Resin ComponentPIL D 13.08 68.18 3.4 BisEMA6 5.77 30.00 1.5 CPQ 0.03 0.17 0.009 EDMAB0.10 1.00 0.025 DPIHFP 0.19 0.50 0.05 BHT 0.03 0.15 0.008 Part B—Zr/Si80.77 NA 21 filler Total 100 100 26

Example 7 Dental Composite

Wt-% Total Wt-% Composition Resin grams Part A—Resin Component PIL D20.45 98.18 4.909 CPQ 0.04 0.17 0.0085 EDMAB 0.10 0.50 0.025 DPIHFP 0.211.00 0.05 BHT 0.03 0.15 0.0075 Part B—Zr/Si 79.17 NA 19 filler Total 100100 24 DTS Std. Shrink- Std. Hard- Std. (MPa) Dev. age, vol % Dev. nessDev. Example 6 92.3 5.5 1.84 0.03 86.2 1.3 Example 7 85.6 5.2 1.84 0.0287.6 1.1 Control 95.3 7.1 1.89 0.02 85.5 1.4 Dental Composite

Example 8 Dental Composite

Wt-% Total Wt-% Composition Resin grams Part A—Resin Component PIL D9.06 48.20 2.41 UDMA 8.46 45.00 2.25 TEGDMA 0.94 5.00 0.25 CPQ 0.03 0.170.0085 EDMAB 0.09 0.50 0.025 DPIHFP 0.19 1.00 0.05 BHT 0.03 0.15 0.0075Part B—Zr/Si 81.20 NA 21.6 filler Total 100 100 26.6 DTS Std. Shrink-Std. Hard- Std. (MPa) Dev. age (%) Dev. ness Dev. Example 8 104 4.5 2.00.04 85.3 1.6 Control 88.6 6.3 1.9 0.02 86.5 1.0 Dental Composite

Example 9 Dental Composite

Wt-% Total Composition Wt-% Resin grams Part A—Resin Component PIL D11.47 48.18 2.409 UDMA 8.57 36.00 1.8 TEGDMA 3.33 14.00 0.7 CPQ 0.040.17 0.0085 EDMAB 0.12 0.50 0.025 DPIHFP 0.24 1.00 0.05 BHT 0.04 0.150.0075 Part B—20 7.62 NA 1.6 nm silica nanomer filler Part B—Zr/Si 68.57NA 14.4 nano cluster filler Total 100 100 21.0

Liquid components were mixed at 3500 rpm for 2.5 minutes, and formed aclear solution. 1.0 g 20 nm silica nanomer filler and 9.0 g Si/Zrnano-cluster filler were mixed first, then added into the resin, speedmixed at 2000 rpm for 1 minute, then speed mixed at 3500 rpm for 2minutes. 20 nm Si nanomer filler (0.3 g) and Si/Zr nano-cluster filler(2.97 g) were added, then speed mixed at 3500 rpm for 2 minutes. 20 nmSi nanomer filler (0.3 g) and Si/Zr nano-cluster filler (2.70 g) wereadded then speed mixed at 3500 rpm for 2 minutes, to give the finalpaste.

Control is Filtek™ Supreme Universal Restorative Composite

Std. Std. DTS (MPa) Dev. Shrinkage Dev. Example 9 73.0 7.9 1.9 0.02Control 81.1 3.3 1.9 0.02 Dental Composite

UV Cure Clear Coating Examples:

The indicated polymerizable ionic liquid, other monomers (HEMA orTEDGMA, from Aldrich) and UV initiator (TPO-L, available from BASF, orDarocur 1173 from Ciba) were mixed in a speed mixing cup to form clearsolution. A drop of coating material was dropped on glass slides withcotton tipped applicator and let the solution spread out with theapplicator. Coated glass slides were passed through a Fusion F 300 UVcuring line under air atmosphere. A UV H-bulb was used and UV intensitywas measured at 9 fpm in air as following, total energy dentist(mJ/cm²), UVA was 1004, UVB was 987, UVC was 153, UVV was 1232.

Using nitrile gloves, the cured coating was touched by hand to check thecuring degree. The curing degree was rated as cure or no cure, andsurface inhibition was rates as no coating liquid smear layer transferor smear layer transfer to glove. Detailed formulation, curing speed andcuring results is listed in the following table.

Wt Photo Wt PIL Wt (g) Other Monomer (g) initiator (mg) 23 fpm 9 fpm Ex.10 0.805 TEGDMA 0.207 Lucerin 29.2 Cured - Cured - PIL-C TPO-L notransfer no transfer Ex. 11 0.886 TEGDMA 0.200 Darocur 28.6 Cured -Cured - PIL-C 1173 no transfer no transfer Ex. 12 0.772 TEGDMA 0.191Lucerin 31.0 Cured - Cured - PIL-D TPO-L no transfer no transfer Ex. 130.828 TEGDMA 0.194 Darocur 28.8 Cured - Cured - PIL-D 1173 no transferno transfer Ex. 14 0.893 TEGDMA 0.106 Lucerin 29.1 Cured - Cured - PIL-ATPO-L no transfer no transfer Ex. 15 0.902 TEGDMA 0.106 Darocur 31.2Cured - Cured - PIL-A 1173 no transfer no transfer Ex. 16 0.803 HEMA0.209 Lucerin 30.4 Cured - Cured - PIL-C TPO-L no transfer no transferEx. 17 0.817 HEMA 0.198 Darocur 30.1 Cured - Cured - PIL-C 1173 notransfer no transfer Ex. 18 0.849 HEMA 0.202 Lucerin 28.8 Cured -Cured - PIL-D TPO-L transfer transfer Ex. 19 0.799 HEMA 0.204 Darocur28.8 Cured - Cured - PIL-D 1173 no transfer no transfer Ex. 20 0.735TEGDMA 0.292 Lucerin 30.0 Cured - Cured - PIL-C TPO-L no transfer notransfer Ex. 21 0.714 TEGDMA 0.299 Darocur 29.3 Cured - Cured - PIL-C1173 no transfer no transfer Ex. 22 0.716 TEGDMA 0.293 Lucerin 30.0Cured - Cured - PIL-D TPO-L transfer transfer Comp A 0 TEGDMA 1.00Lucerin 32 NA partially TPO-L cured - transfer Comp B 0 TEGDMA 1.01Darocur 26 NA partially 1173 cured - transfer Comp C 0 HEMA 1.01 Lucerin30 NA partially TPO-L cured - transfer Comp D 0 HEMA 1.01 Darocur 30 NApartially 1173 cured - transfer Comp E 0 BisGMA/TEGDMA 1.00 Lucerin 32NA partially (50/50) TPO-L cured - transfer NA 0 BisGMA/TEGDMA 1.00Darocur 30 NA partially (50/50) 1173 cured - transfer

The results show that the inclusion of a polymerizable ionic liquid canimprove the curing in air. Examples 13, 18, 19, and 22 demonstrate thatDarocur 1173 photoinitiator is preferred for blends of HEMA or TEGMAwith PIL-D.

UV Cured White Colored Coating Examples:

The indicated polymerizable ionic liquid, TEGDMA, titanium dioxide(TiO₂) and UV initiator (Darocur 1173 from Ciba) were mixed in a speedmixing cup to form white color coating composition. A drop of coatingmaterial was applied on glass slides with cotton tipped applicator andlet the solution spread out with the applicator. Coated glass slideswere passed through a Fusion F 300 UV curing line under air atmosphere.A UV H-bulb was used and UV intensity was measured at 9 fpm in air asfollowing, total energy dentist (mJ/cm²), UVA was 1004, UVB was 987, UVCwas 153, UVV was 1232.

A cotton-tipped applicator was used to touch the sample after curing tocheck the curing degree. The curing degree was rated as cure or no cure.Detailed formulation, curing speed and curing results were listed in thefollowing table.

Composition PIL TiO₂ UV Wt Wt TEGDMA Initiator Curing line speed andcuring results PIL (g) (g) Wt (g) Wt (mg) 3 fpm 9 fpm 23 fpm PIL- 2.00.30 NA 0.0690 Surface Cured - Surface Cured - Surface Cured - D WhiteWhite White PIL- 2.0 0.30 NA 0.0730 Surface Cured - Surface Cured -Surface Cured - A Tan Tan White PIL- 1.8 0.30 0.20 0.0650 SurfaceCured - Surface Cured - Surface Cured - D Tan Tan White PIL- 1.8 0.300.20 0.0680 Surface Cured - Surface Cured - Surface Cured - A Tan TanWhite PIL- 1.6 0.30 0.40 0.0700 Surface Cured - Surface Cured - SurfaceCured - D Tan Tan White PIL- 1.1 0.20 0.28 0.0457 Surface Cured -Surface Cured - Surface Cured - A White White White Comp 0.0 0.30 2.000.0680 not cured not cured not cured

1. A curable composition comprising at least one polymerizable ionicliquid having an air to nitrogen curing exotherm ratio of at least 0.70and at least one other ethylenically unsaturated monomer, oligomer, orpolymer.
 2. The curable composition of claim 1 wherein the polymerizableionic liquid is a multifunctional polymerizable ionic liquid comprisingat least two ethylenically unsaturated groups.
 3. The curablecomposition of claim 2 wherein the polymerizable ionic liquid furthercomprises is a monofunctional polymerizable ionic liquid.
 4. The curablecomposition of claim 2 wherein the polymerizable ionic liquid has an airto nitrogen curing exotherm ratio of at least 0.90.
 5. The curablecomposition of claim 1 wherein the other ethylenically unsaturatedmonomer(s), oligomer(s), or polymer(s) has an air to nitrogen curingexotherm ratio of no greater than 0.50. 6-12. (canceled)
 13. The curablecomposition of claim 12 wherein the curable compositions comprises aphotoinitiator.
 14. The curable composition of claim 1 wherein thepolymerizable ionic liquid comprises a substituted ammonium cationicgroup.
 15. The curable composition of claim 1 wherein the polymerizableionic liquid comprises a sulfonate anion.
 16. The curable composition ofclaim 1 wherein the polymerizable ionic liquid comprises an anion, acationic group, and at least two ethylenically unsaturated groups bondedto the cation.
 17. The curable composition of claim 16 wherein thepolymerizable ionic liquid comprises an anion, a cationic group, and atleast two ethylenically unsaturated polymerizable groups, each bonded tothe cationic group via a divalent non-alkylene linking group. 18-20.(canceled)
 21. The curable composition of claim 1 wherein thepolymerizable ionic liquid comprises a polymerizable anion.
 22. Thecurable composition of claim 21 wherein the polymerizable ionic liquidcomprises a polymerizable anion and a polymerizable cation.
 23. Thecurable composition of claim 1 wherein the polymerizable ionic liquidcomprises an aromatic carboxylate anion.
 24. The curable composition ofclaim 23 wherein the cation comprises a free-radically polymerizablegroup and the anion lacks a free-radically polymerizable group.
 25. Thecurable composition of claim 23 wherein the anion comprises afree-radically polymerizable group and the cation lacks a free-radicallypolymerizable group.
 26. The curable composition of claim 23 wherein theanion and cation each comprise at least one free-radically polymerizablegroup.
 27. The curable composition of claim 23 wherein the cation is asubstituted ammonium, phosphonium, imidazolium cation.
 28. An articlecomprising the cured composition of previous claim
 1. 29. An articlecomprising a substrate and the cured coating composition of claim 1disposed on a surface of the substrate. 30-34. (canceled)
 35. Amonofunctional polymerizable ionic liquid comprising a non-polymerizablesubstituted imidazolium cationic group and a polymerizable sulfonateanion. 36-37. (canceled)